<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<script>
window.onload=function ()
{
	var oBtn1=document.getElementById('btn1');
	var oBtn2=document.getElementById('btn2');
	var timer=null;
	
	oBtn1.onclick=function ()
	{
		timer=setInterval(function (){
			alert('a');
		}, 1000);
	};
	
	oBtn2.onclick=function ()
	{
		clearInterval(timer);
	};
};
</script>
</head>

<body>
<input id="btn1" type="button" value="开启" />
<input id="btn2" type="button" value="关闭" />
</body>
</html>
